Question

如果栏中不相等，我怎么能使用“IN”。

LEFT JOIN (
     SELECT student_id 
     FROM students 
     WHERE student_id  IN (
             SELECT student_id,
                    CASE 
                       WHEN (
                          //condition           
                       )
                       THEN 'Yes'
                       ELSE 'No'
                    END AS refusal
             FROM refusal_field
 )
) AS a USING(student_id)

它说：子查询有太多列

我真的需要“拒绝”专栏给我LEFT JOIN。怎么做？

Answer 1

这样的事情怎么样？这应该有你想要的结果：

LEFT JOIN (
SELECT student_id,
CASE 
WHEN (
//condition         
)
THEN 'Yes'
ELSE 'No' 
END AS refused
FROM students 
INNER JOIN refusal_field ON refusal_field.student_id = students.student_id)

Answer 2

实际上，子查询有两列：student_id和拒绝，它应该只有student_id，我相信你想要的是：

LEFT JOIN (
   SELECT 
      student_id,
      CASE 
         WHEN (
          //condition         
         ) THEN 'Yes'  ELSE 'No' END AS refusal
   FROM students WHERE student_id  IN (
      SELECT student_id
      FROM refusal_field
   )
) AS a USING(student_id)

在列中不相等时使用“IN”

2 个答案: